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Claudine Habak, Frances Wilkinson, Hugh R. Wilson; Spatial frequency dependence in contextual modulation of shape. Journal of Vision 2004;4(8):667. doi: https://doi.org/10.1167/4.8.667.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Previous work using deformed circular contours (radial frequency (RF) patterns) has shown that contextual interactions exist among such patterns: perceived deformation from circularity of an RF pattern can be influenced by a concentric RF pattern of higher amplitude. This influence is consistent with global but not local interactions. In order to assess further the contribution of various processing stages, the present work examines the range over which interactions occur for target and mask of differing spatial frequency. Methods: Thresholds for detecting deviations from circularity were measured for a target RF pattern with 5 cycles (RF5, radius 1.14 deg, peak spatial frequency 8cpd) when the pattern was shown alone and with a mask. Masks consisted of an RF5 pattern surrounding the target and had one of 4 peak spatial frequencies 2, 4, 8, and 16 cpd. Mean target-mask distance was 0.29 deg. Observers discriminated deviations from circularity in a 2IFC paradigm using the method of constant stimuli. Results: Thresholds were elevated by a factor of 2–3 for target and mask of identical spatial frequency (8 cpd). Masking, though weaker, occurred over the entire range of spatial frequencies tested (threshold elevations of 1.5–2.2). Additional effects of contrast were evaluated. Conclusions: Spatial frequency interactions in contextual modulation of perceived deformation from circularity reveal that masking was found up to at least 2 octaves, unlike traditional experiments of V1-dependent masking, and are consistent with an intermediate-level (V4) processing site.
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